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  • Updated 11.21.2023
  • Released 09.21.1998
  • Expires For CME 11.21.2026

CNS listeriosis



Listeriosis is a rare but important disease, usually causing a mild self-limited gastroenteritis, but rarely an invasive dangerous bacteremia, meningitis, or meningoencephalitis. Pregnancy-associated listeriosis can be missed as a minor infection in the mother but can cause miscarriage or severe illness in the fetus or infant.

CNS listeriosis has the second highest case fatality rate amongst food-borne diseases. Almost one third of all patients die despite adequate therapy, and hardly one third survive unscathed.

It is very important to realize that this preventable and treatable disease is almost always acquired (99% of cases) by eating infected food (72).

This fascinating bacillus can tenaciously survive adverse environments, biding time for years in a dormant form like a saprophyte. When conditions are right, it can awaken, multiply rapidly, silently invade the host, and suddenly transform into a dangerous pathogen targeting infants and elderly, pregnant women, or sick and immunocompromised persons, with a particular affinity for the brain, causing meningitis, meningoencephalitis, or abscesses (80). It uses unique mechanisms to breach defenses, evade the immune system, reach the bloodstream, and travel backward to the brainstem via the vagus and trigeminal nerves.

Pregnancy by itself puts women at a very high risk of getting Listeria infection. A deceptively minor-looking febrile illness in the mother may target and severely affect the unborn or newborn baby (72). One must know about the uncommon Listeria rhombencephalitis, which presents as a benign-looking illness in healthy young adults. If it is missed at this early stage or there is a delay in diagnosis, it rapidly progresses to bulbar and respiratory paralysis, and often death.

Finally, it is important to remember that Listeria responds mainly to certain older antibiotics like penicillins, aminoglycosides, or trimethoprim-sulfamethoxazole. Most newer antibiotics, like cephalosporins, fail.

We can ignore Listeria only at our peril. I have been extremely lucky to escape an attack of Listeria rhombencephalitis.

Key points

• CNS listeriosis is a rare but important disease with the second highest case-fatality rate amongst food-borne diseases.

• Almost all cases are caused by eating contaminated food.

• In most exposed persons, it only causes a self-limited gastroenteritis.

• Persons at risk of invasive disease include the elderly and infants, immunocompromised persons, diabetics, and cancer patients.

• One third with invasive disease die, and another one third have major disability. Hardly one third escape without any major disability.

• Pregnant women are at very high risk of listeriosis. The illness in women is mild and looks like an innocuous flu-like illness, but it can seriously hurt or even kill the fetus.

• Listeria has the unique ability to silently evade various defense mechanisms, cross barriers, and move intracellularly and within axons.

• Rhombencephalitis is a deceptive but extremely dangerous form, often seen in healthy and young persons.

• Those at high risk need to know particularly about food choices and food handling.

• Risky foods include dairy products, fruits and vegetables, meat products, fish products, and even hospital foods.

• A high index of suspicion and early treatment are the key to success.

• The therapy of choice for CNS listeriosis is combination therapy. The first choice is a beta-lactam (ampicillin or benzylpenicillin), combined with gentamicin or with TMP-SMX. If beta-lactam is contraindicated, then one uses TMP-SMX plus gentamicin. Meropenem comes in only when both beta-lactams and gentamicin are contraindicated.

• The duration of therapy in CNS listeriosis should be at least 3 to 4 weeks in immunocompetent and 6 to 8 weeks in immunosuppressed persons.

• Studies suggest that steroids, when started with the antibiotics, are beneficial.

Historical note and terminology

Listeria monocytogenes has long been recognized as a veterinary pathogen causing basilar meningitis and stillbirth in sheep and cattle. It was first described as human pathogen in a patient with a mononucleosis-like syndrome in 1929 (89).

Meningitis due to L. monocytogenes was described in 1936, but the first authentic isolation came from a World War I soldier in 1918. His meningitis was attributed to a diphtheroid species. However, the original culture was preserved at the Pasteur Institute in Paris and was identified 20 years later as L. monocytogenes. This historical note provides an important reminder that L. monocytogenes is sometimes confused and dismissed as a diphtheroid contaminant because of morphological, colonial, and biochemical similarities. A 1949 German epidemic of “granulomatosis infantisepticum” led to the discovery that L. monocytogenes caused this severe neonatal infection (45). Brainstem encephalitis or rhombencephalitis due to Listeria was first described in 1957 (33). The first foodborne listeriosis outbreak was attributed to infected vegetables in a Boston Hospital in 1979 (38).

This gram-positive bacterium has been known by many names, including Listerella hepatolytica, Corynebacterium infantisepticum, Corynebacterium parvulum, and Erysipelothrix monocytogenes. In 1940, taxonomists reached a general agreement to call the species Listeria monocytogenes in honor of the father of antisepsis, Lord Lister (103).

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